Diffusion tower

ABSTRACT

A DIFFUSION TOWER FOR THE EXTRACTION OF JUICES FROM SUGAR BEET COSSETTES IS PROVIDED AT ITS LOWER END WITH SIEVE OR SCREEN WORM MEANS WHICH ARE SUPPORTED IN RESPECTIVE HOUSINGS AT ONE END THEREOF SO AS TO REACH WITH ITS FREE, OVERHANG END TOWARD AN OPENING IN THE TOWER WHEREBY THE TOWER FACING TURN OF THE SCREEN WORM MEANS KEEPS THE   COSSETTES IN THE TOWER AND PERMITS THE ESCAPE OF THE JUICE. EACH HOUSING COMPRISES A SIEVE OR SCREEN AREA, PREFERABLY A CYLINDRICAL SIEVE SURROUNDING THE SCREEN WORM PROPER. AT LEAST ONE OF THE WORMS IS PROVIDES WITH A SOLID WING FOR THE INFEED OF THE SUGAR BEET COSSETTES INTO THE TOWER.

v' Feb. 26, 1974 DIETZEL EIFAL 3,794,521

DIFFUS I 0N TOWER Filed Jan. 10, 1972 2 Sheets-Sheet 1 Feb. 26, 1974 w, DlETZEL ETAL 3,794,521

Q DIFFUSION TOWER Filed Jan. 10, 1972 2 Sheets-Sheet 2 United States Patent Office 3,794,52l Patented Feb. 26, 1974 3,794,521 DIFFUSION TOWER Walter Dietzel and Siegfried Matusch, Braunschwelg, Germany, assignors to Braunschweigische Maschmenbauanstalt, Braunschweig, Germany Filed Jan. 10, 1972, Ser. No. 216,496 Claims priority, application Germany, Feb. 11, 1971, P 21 06 464.2; Jan. 15,1971, G 71 01 390.6

Int. Cl. C13d 1/12 US. Cl. 127-5 8 Claims ABSTRACT OF THE DISCLOSURE A diffusion tower for the extraction of juices from sugar beet cossettes is provided at its lower end with sieve or screen worm means which are supported in respective housings at one end thereof so as to reach with its free, overhang end toward an opening in the tower whereby the tower facing turn of the screen worm means keeps the cossettes in the tower and permits the escape of the juice. Each housing comprises a sieve or screen area, preferably a cylindrical sieve surrounding the screen worm proper. At least one of the worms is provided with a solid wing for the infeed of the sugar beet cossettes into the tower.

BACKGROUND OF THE INVENTION The invention relates to a diffusion tower for the continuous countercurrent extraction of juice from sugar beet cossettes, the mixed cossettes being fed into the tower at the bottom thereof and the pulp being discharged at the top of the tower.

Due to technological conditions during leaching of sugar beet cossettes in a-diffusion tower, the zone in which the juice has the highest sugar content is located at the bottom part of the diffusion tower because feeding of the fresh sugar beet cossettes to be leached is effected at that point and these sugar beet cossettes have the highest sugar content.

The diffusion towers of the prior art are equipped with a so-called screen section at the bottom in order to discharge the juice from the inside of the diffusion tower at the point where the juice has the highest sugar content. A conical screen bottom is located in this screen section as bottom limit of the diffusion tower filled with a cossetteliquid mixture.

The discharge of liquid. through these screens is only possible if mechanical scrapers are, in the known diffusion towers, attached to the bottom end of the conveyor shaft. These scrapers or blades move in contact with the screens and guarantee that the screen holes are kept open. Due to this operation of the scrapers, the screen areas are subject to a strong wear on account of the scrapers sliding continuously in contact with the screens. This wear is still increased by said particles in the cossette-liquid mixture.

The screen section of the diffusion tower also includes drical shell of the bottom tower end and which are also permanently cleaned from sugar beet cossettes by respective scrapers or blades.

These screens or the screen section were often damaged in the past and this resulted in considerable operation troubles since the screens could only be repaired after the diffusion tower had been emptied.

In order to avoid this disadvantage, a so-called screenless diffusion tower has already been suggested in which the screens necessary for the separation of liquid and cossettes were located in a lateral zone outside the tower. Special liquid separators have been used in this type of tower and these separators are connected to the inside of the tower by feed pipes with built-in stop elements. These liquid separators were provided with screen areas and conveyor means which drag the cossette-juice mixture over the screen areas. The conveyor means also assure the return of the cossettes to the inside of the tower. The movement of these conveyor means was to remove cossettes adhering to the screen areas. The stop elements installed in the feed pipe connected to the inside of the tower between these liquid separators were supposed to permit the disconnection of defective liquid separators during failures such as damaged screen areas, from the inside of the diffusion tower by closing the stop elements. The purpose of this arrangement was to repair screens of individual liquid separators without interrupting the operation of the diffuser.

However, this proposal-a diffusion tower without bottom screens-was not put into practice because on the one hand, interruptions of operation due to defective screens occurred less frequently due to improved screen sections, and on the other hand, uncontrollable working conditions arose in the diffusion zone of the screen section.

In connection with one conventional tower construction, the cossette-liquid mixture entering the liquid separator for liquid separation had to enter through the same connecting element through which the cossettes considerably poorer in liquid after the liquid separation had to be returned to the inside of the tower. These flows in opposite directions through a relatively narrow flow cross section made flow interference unavoidable. Furthermore, dead zones could be formed in the inside of the tower. A different type of this suggested diffusion tower provided separate flow ways for the cossette-liquid mixture entering the liquid separators from the inside of the tower and reentering the inside of the tower after the lequid separation; however, even this arrangement did not guarantee controllable flow conditions inside the screen section. Moreover, the passage of the cossette-liquid mixture through the relatively narrow connecting pipes with stop elements in these pipes subjected the cossettes to a mechanical stress which resulted in a high proportion of pulp due to wear and destruction of the cossettes.

Thus, it was not possible to obtain a particularly gentle and uniform leaching of all cossettes fed into the above described diffusion tower. Disadvantages occurred although the sugar yield was increased, i.e., leaching was improved. Every increase in sugar yield and improvement of leaching, respectively-even if it is very smallobtained by economical means represents a considerable profit in practice.

OBJECTS OF THE INVENTION The present invention has for its object to improve a diffusion tower of the screen type in such a way that the efficiency of juice separation is improved by movable screen areas located outside the inner space of the tower ugiile simultaneously avoiding the disadvantages described a ove.

SUMMARY OF THE INVENTION According to the invention there are provided screen form means with worm shaft means supported in an overhung and mainly horizontal position adjacent the bottom tower part. At least the turn of the warm facing a respective lateral opening in the tower is provided with screen apertures to keep the cossettes in the tower and let the juice escape. One worm is provided with flights or turns without any apertures to feed the cossette-juice mixture into the tower, whereas the other screen worm means exclusively serve for the juice separation and are thus provided with band-type flights in addition to said one apertured turn or flight of the screen worm serving for the juice separation is constructed as a screen area extending from the inside edge of the band-type flight to the worm shaft.

The feeding of the cossette-liquid mixture by means of an open ended worm having flights Without apertures results in a gentle treatment of the cossettes so that pulping is avoided because squeezing of the cossettes due to flow passage areas of reduced cross sectional size is eliminated. Similar considerations apply to the screen worm means serving for the juice separation which may be distributed about the circumference of the tower near its bottom.

The special construction of the screen worms for the juice separation is an important characteristic of the present invention, since the band type flights of these worms keep the surrounding screen areas clean, whereas the screen area located at the open end between the band type flight and the worm shaft separates the space inside the band type flights from the tower inside. This feature prevents cossettes from entering the space within the band-type flights; however, entering of juice is not prevented. Cossettes moving towards the inside of the screen worm through the gap between the worm screen area and the respective opening in the tower are again discharged by the transport movement of the band type flights. The screen holes of the screen areas are kept free by the permanent movement even without mechanical scrapers.

An advantage of the invention is seen in the considerable improvement in the leaching. Flow and movement conditions are clearly visible in the zone of the bottom section, and a largely uniform leaching of all cossettes is guaranteed.

The communication between the inside of the screen worms and the inside of the diffusion tower for the juice removal is especially advantageous if the diameter and the axial length of the screen worms are about equal to each other.

Arranging the shafts of the screen worms at a slightly inclined angle towards the tower radius has the advantage that the rotation of the conveyor shaft in the tower tends to entrain the cossettes which facilitates the smooth transit into the range of influence of the conveyor shaft inside the tower. Concerning the screen worms exclusively serving for the juice separation, the flow of the juices in the bottom section of the tower can be favorably influenced by this inclined position. However, the angle of inclination must not be too large in order to avoid dead flow zones.

BRIEF FIGURE DESCRIPTION One example embodiment of the diffusion tower according to the invention is illustrated in the drawings, wherein:

FIG. 1 shows an elevational view partially in section of the bottom range of the diffusion tower according to the invention,

FIG. 2 shows somewhat schematically a cross section through the bottom part of the diffusion tower according to the invention, wherein the worm means, for facilitating the illustration, are shown on a larger scale than the tower itself; and

FIG. 3 shows a schematic front view of a screen worm exclusively serving for the juice separation.

DESCRIPTION OF AN EXAMPLE EMBODIMENT The FIGS. 1 and 2 show a diffusion tower 1 for the continuous countercurrent extraction of juice from sugar beet cossettes. The diffusion tower 1 has the form of an upright cylinder and comprises a bottom section 2 and several body sections 3 of almost the same structure. The top end with the equipment for discharging the leached pulp is not shown. A conveyor shaft 4 mechanically driven at the top and/or bottom end is provided concentrically inside the diffusion tower 1.

Transporting flights 5 attached to the conveyor shaft 4 and cooperating with adjustable guide flights 6 which are attached to the body sections 3 produce transporting forces when the conveyor shaft is rotated to move the mixture of sugar beet cossettes and liquid in ascending direction through the diffusion tower 1.

The leaching liquid is fed into the top part of the diffusion tower 1 and flows from top to the bottom, i.e. opposite to the movement of the cossettes through the diffusion tower 1. The liquid enriched with sugar which is discharged as so-called circulation juice in the zone of the bottom section 2 of the diffusion tower 1, is heated and mixed with the fresh sugar beet cossettes. Part of this juice is separated by the cossette mixer and transported as socalled feed juice to further processing stations, while the remainder of this liquid, namely the circulation juice, is mixedwith heated cossettes in order to produce a mixture which can be pumped by a cossette pump, not shown, into the bottom section 2 of the diffusion tower 1.

The worms 7 and 8 separate the juice according to the invention. These worms have a worm shaft 9 supported in an overhung position so that the free end of the worm faces into the tower through a respective opening without any reduction in flow cross sectional area. The worms 7, 8 with their horizontal worm axles are spaced at intervals around the circumference of the bottom section 2. A bearing 10 with respective gaskets supports and seals its shaft 9. Gear units 11 are provided as drives. The drive speeds can vary from 20 to 60 rpm.

Every worm 7, 8 is surrounded with a screen shell 12 which is provided with a pipe 13 to discharge the juice.

At least one worm 7 has a pipe connection 14 through which the cossette-juice mixture is fed into the worm housing by means of a cossette pump. As this worm 7 conveys the cossettes into the tower, it is equipped with solid flights or wings 15 without any apertures. All worms are surrounded by screens 12 for the escape of the juice. The worms are provided with a band wing 8 helically surrounding the shaft 9 and with an apertured wing 23 facing a lateral opening in the tower.

The screen worms 8 for the juice separation have a relatively large free space between the inside edge of the band wing 8' and the worm shaft 9. This free space is covered by a screen or apertured area 23, for instanc a screen plate which is arranged in such a way that it extends from the inside edge of the band wing 8' to the free end of worm shaft 9, so as to face a respective opening in the tower over a 360 area.

The shafts of the worms 7 and 8 are generally located radially relative to the diffusion tower 1. Slight inclinations as shown at the bottom of FIG. 2 may be advantageous if no dead spaces occur in which the cossette movement is slowed down or comes to a stand-still.

For a gentle treatment of the cossettes and for obtaining smooth flows it is advantageous if the diameters of the worms 7, 8 are notas it is conventionally the case--small in comparison to the length. Preferably, the worm length and the worm diameter are about the same.

The bottom of bottom section 2 of the tower is provided with at least one sand catcher 20 which is equipped with a continuously working or batch type sand discharging device 21. The funnel type tank of the sand catcher 20 is connected with the inside of the diflusion tower by means of suitable screens 22 which are kept clean by the distributor of the conveyor shaft 4 or the scrapers attached to it.

We claim:

1. In a diffusion tower for the continuous countercurrent extraction of juice from sugar beet cossettes in which the cossettes are fed into said tower at its bottom end, wherein leached cossettes are discharged at the top end of the tower, and wherein the sugar-enriched extracted juice is removed through screen means arranged at the bottom of the tower, the improvement comprising lateral openings at the bottom end of said tower, said screen means comprising movable screen areas, means for movably supporting said screen areas relative to said lateral openings to substantially close the openings against the escape of cossettes but to permit the escape of the juice through said movable screen means, and drive means operatively connected to said movable screen areas to keep these screen areas in motion when the tower is in operation.

2. The diffusion tower according to claim 1, further comprising cossette supply worm means arranged to face one; of said openings in said tower, and drive means operatively connected to said cossette supply worm means to rotate said supply worm means in such a direction as to feed cossettes into the tower.

3. The diffusion tower according to claim 1, further comprising worm means and respective worm shaft means, said movable screen areas forming substantially one turn of said worm means on said worm shaft means, means for rotatably supporting said worm shaft means in such a position relative to the tower that said one turn screen area of the worm means faces a respective one of said lateral openings in the tower, said drive means being operatively connected to said worm shaft means for rotating said worm means in such a direction as to keep the cossettes in the tower.

4. The diffusion tower according to claim 3, wherein said worm means comprise in addition to said substantially one turn screen area, band-shaped wing means extending helically about said shaft means from said one turn screen area to the end of the worm means.

5. The diffusion tower according to claim 3, wherein said worm means have a diameter and an axial length substantially equal to each other.

6. The diffusion tower according to claim 3, wherein said shaft means of the worm means are slightly inclined relative to a radius of the tower.

7. The diffusion tower according to claim 3, further comprising worm housing means in which said worm means and worm shaft means are supported at one end thereof so that the free end with said one turn screen area faces its respective lateral opening in the tower.

8. The diffusion tower according to claim 7, comprising a plurality of said worm housing means distributed about the circumference of said tower adjacent the bottom thereof.

References Cited UNITED STATES PATENTS 2,183,837 12/1939 Hamilton 23-270 R 2,158,782 5/1939 Bonotto 23-270 R 2,502,939 4/1950 Frynta 127-5 2,602,761 7/1952 Hildebrandt 23-170 R X 2,645,589 7/1953 Langen 23-270 R X 2,663,623 12/1953 Anderson 23-270 R 2,928,760 3/1960 Christoffersen 127-5 X 3,142,589 7/1964 Schaffer 127-5 X 3,432,344 3/1969 Farmer 127-5 X MOR RIS 0. WOLK, Primary Examiner S. MARANTZ, Assistant Examiner US. Cl. X.R. 23-270 R 

